Direct injection of fuel in which fuel is delivered directly into a combustion chamber of an engine may be employed to deliver fuel to an engine. The fuel injector may receive high pressure fuel from a rail pressurized by a high pressure fuel pump. Direct injection may enable flexibility in the timing of fuel delivery into the cylinder depending on operation conditions.
The inventors herein have recognized during hot engine restarts, a higher than requested fuel flow may be delivered to the engine due to the high pressure in the fuel rail from the high temperature fuel, along with minimum opening times of the injector. As such, air-fuel ratio may be not maintained at a desired level due to the increased amount of fuel delivered to the engine. As a result, efficient emission control may be reduced, as emissions from the engine may increase.
Thus in one example, the above issues may be at least partially addressed by a method for an engine. One example method comprises, during a hot engine restart, adjusting fuel injection timing into an engine cylinder such that for an entire duration a fuel injector is open, cylinder pressure is greater than a threshold cylinder pressure. In this way, it is possible to take advantage of the compression generated by the piston during the compression stroke to counteract the effects of the minimum opening time of the injector.
In one example, the threshold cylinder pressure may increase with an increase in a fuel rail pressure. As such, fuel injection opening and closing timings may be retarded as compared to a cold start condition or a hot restart condition where injection timing is not modified significantly based on cylinder pressure. By retarding fuel injection to a condition when the cylinder pressure is greater, the higher cylinder pressure increases a fuel pulsewidth needed to achieve a desired amount of injected fuel for a given rail pressure. In this manner, the fuel pulsewidth may be more easily modified in response to air-fuel ratio demands for emission control, for example.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.